In effecting identification of aircraft modal parameters such as, by way of example and not by way of limitation, structural frequency, damping and mode shape, from flight test time history response data may be difficult because the test data may contain responses from multiple, coupled modes.
One approach to identifying such modal parameters is by manual single degree of freedom evaluating methods such as using a form of logarithmic decrement. Such manual evaluations are unable to properly characterize coupled mode behavior. The results produced by such methods may vary from one sensor to the next as well as from one excitation to the next. Mode shape information is not provided by such methods.
Another approach to identifying such modal parameters is disclosed in U.S. Pat. No. 6,947,858, issued Sep. 20, 2005, to Goodman et al., and assigned to the assignee of the present application (hereinafter referred to as “Goodman '858”). Goodman '858 addressed multiple sensors or gauges for a given excitation and properly characterized coupled mode behavior. This treatment did characterize mode shape. Goodman '858 did not address treating data from a plurality of excitations for a plurality of sensors or gauges. The frequency, damping, and mode shape identification may vary from one excitation to the next with that approach.
There is a need for a method and apparatus for evaluating data, such as flight test data, representing a plurality of excitations of a plurality of sensors.